Support backtrace after method calls

GitHub: fix #2902, #2917

The current implementation traverses stack to retrieve backtrace. But
stack will be changed when some operations are occurred. It means that
backtrace may be broken after some operations.

This change (1) saves the minimum information to retrieve backtrace when
exception is raised and (2) restores backtrace from the minimum
information when backtrace is needed. It reduces overhead for creating
backtrace Ruby objects.

The space for the minimum information is reused by multiple
exceptions. So memory allocation isn't occurred for each exception.

1 files changed, 10 insertions, 8 deletions

diff --git a/src/vm.c b/src/vm.c
index 391646017..b2149b250 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -258,6 +258,8 @@ cipop(mrb_state *mrb)
   c->ci--;
 }
 
+void mrb_exc_set(mrb_state *mrb, mrb_value exc);
+
 static void
 ecall(mrb_state *mrb, int i)
 {
@@ -669,7 +671,7 @@ localjump_error(mrb_state *mrb, localjump_error_kind kind)
   mrb_str_cat(mrb, msg, lead, sizeof(lead) - 1);
   mrb_str_cat(mrb, msg, kind_str[kind], kind_str_len[kind]);
   exc = mrb_exc_new_str(mrb, E_LOCALJUMP_ERROR, msg);
-  mrb->exc = mrb_obj_ptr(exc);
+  mrb_exc_set(mrb, exc);
 }
 
 static void
@@ -688,7 +690,7 @@ argnum_error(mrb_state *mrb, mrb_int num)
                   mrb_fixnum_value(mrb->c->ci->argc), mrb_fixnum_value(num));
   }
   exc = mrb_exc_new_str(mrb, E_ARGUMENT_ERROR, str);
-  mrb->exc = mrb_obj_ptr(exc);
+  mrb_exc_set(mrb, exc);
 }
 
 #define ERR_PC_SET(mrb, pc) mrb->c->ci->err = pc;
@@ -1007,7 +1009,7 @@ RETRY_TRY_BLOCK:
 
     CASE(OP_RAISE) {
       /* A      raise(R(A)) */
-      mrb->exc = mrb_obj_ptr(regs[GETARG_A(i)]);
+      mrb_exc_set(mrb, regs[GETARG_A(i)]);
       goto L_RAISE;
     }
 
@@ -1241,7 +1243,7 @@ RETRY_TRY_BLOCK:
         mrb_value exc;
 
         exc = mrb_exc_new_str_lit(mrb, E_NOMETHOD_ERROR, "super called outside of method");
-        mrb->exc = mrb_obj_ptr(exc);
+        mrb_exc_set(mrb, exc);
         goto L_RAISE;
       }
       recv = regs[0];
@@ -1331,7 +1333,7 @@ RETRY_TRY_BLOCK:
           mrb_value exc;
 
           exc = mrb_exc_new_str_lit(mrb, E_NOMETHOD_ERROR, "super called outside of method");
-          mrb->exc = mrb_obj_ptr(exc);
+          mrb_exc_set(mrb, exc);
           goto L_RAISE;
         }
         stack = e->stack + 1;
@@ -1561,7 +1563,7 @@ RETRY_TRY_BLOCK:
             }
             if (mrb->c->prev->ci == mrb->c->prev->cibase) {
               mrb_value exc = mrb_exc_new_str_lit(mrb, E_FIBER_ERROR, "double resume");
-              mrb->exc = mrb_obj_ptr(exc);
+              mrb_exc_set(mrb, exc);
               goto L_RAISE;
             }
             /* automatic yield at the end */
@@ -2323,7 +2325,7 @@ RETRY_TRY_BLOCK:
       /* A      R(A) := target_class */
       if (!mrb->c->ci->target_class) {
         mrb_value exc = mrb_exc_new_str_lit(mrb, E_TYPE_ERROR, "no target class or module");
-        mrb->exc = mrb_obj_ptr(exc);
+        mrb_exc_set(mrb, exc);
         goto L_RAISE;
       }
       regs[GETARG_A(i)] = mrb_obj_value(mrb->c->ci->target_class);
@@ -2381,7 +2383,7 @@ RETRY_TRY_BLOCK:
       else {
         exc = mrb_exc_new_str(mrb, E_LOCALJUMP_ERROR, msg);
       }
-      mrb->exc = mrb_obj_ptr(exc);
+      mrb_exc_set(mrb, exc);
       goto L_RAISE;
     }
   }